JP3182255B2 - Non-aqueous electrolyte battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte battery, and more particularly, to prevent deterioration of storage characteristics and cycle characteristics due to degradation of a solvent in a non-aqueous electrolyte on a positive electrode side. And improvement of the non-aqueous electrolyte.

[0002]

2. Description of the Related Art In recent years,
Non-aqueous electrolyte batteries such as lithium batteries are different from batteries that use aqueous electrolytes such as nickel-cadmium batteries,
Since it is not necessary to consider the decomposition voltage of water, a high voltage design of usually 3 V or more is possible, which is attracting attention.

[0003] As the positive electrode active material of such a high-voltage nonaqueous electrolyte battery, manganese, cobalt, and the like are generally used.
Oxides of metals such as nickel, vanadium, and niobium or composite oxides containing two or more of these metals have been used.

However, the above-mentioned metal oxide or composite oxide easily reacts with the non-aqueous electrolyte, so that the solvent in the non-aqueous electrolyte is decomposed during storage of the battery, and the decomposition product (polymer) Etc.) adhere to the electrodes, and as a result, the internal resistance (internal impedance) of the battery after storage increases and the discharge characteristics decrease, and in the case of a secondary battery, the cycle characteristics further decrease. There was a problem. Incidentally, such a decomposition reaction of the solvent occurs remarkably when the positive electrode is charged at a high potential.

[0005] By the way, attempts to improve the storage characteristics and the cycle characteristics by suppressing the above-mentioned decomposition reaction of the solvent have been made in the past. For example, tetrahydrofuran (TH
F), attempts have been made to substitute a part of hydrogen atoms of a cyclic ether such as 1,3-dioxolane (DOXL) with an alkyl group and the like to stabilize the hydrogen atom and to make it difficult to decompose and degrade (J.
L. Goldman, RM Mank, JH Young and VR Koc
h: J. Electrochem. Soc., 127,1461 (1980)).

However, it is difficult to stabilize the non-aqueous electrolyte sufficiently even by such modification of the cyclic ether by alkylation, and it is necessary to effectively suppress the decomposition reaction of the non-aqueous electrolyte on the high potential positive electrode side. The fact is that it has not been reached. In particular, in the case of a secondary battery, it has been pointed out that during overcharging, a decomposition reaction of a solvent accompanied by generation of carbon dioxide gas or the like proceeds rapidly on the positive electrode, and the battery characteristics are significantly deteriorated.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a non-aqueous electrolyte battery having excellent battery characteristics such as storage characteristics and cycle characteristics.

[0008]

In order to achieve the above object, a non-aqueous electrolyte battery according to the present invention (hereinafter, referred to as "battery of the present invention") comprises a metal lithium or a substance capable of occluding and releasing lithium. In a non-aqueous electrolyte battery including a negative electrode as a material, a positive electrode, and a non-aqueous electrolyte, an azo compound represented by the following formula (2) is added to the non-aqueous electrolyte.

[0009]

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However, R ¹ , R ² , R ³ and R ⁴ are each independently a hydrogen atom or a hydrocarbon group.

Specific examples of the azo compound in the present invention include 4,4'-tetramethyldiaminoazobenzene,
4,4′-tetraethyldiaminoazobenzene, 4,
4'-tetrapropyldiaminoazobenzene, 4,4 '
-Tetrabutyldiaminoazobenzene and 4,4'-tetraphenyldiaminoazobenzene. These azo compounds may be used alone or in combination of two or more as needed.

The azo compound in the present invention must be a substance whose oxidation potential is more noble than the charge voltage of the battery and lower than the decomposition voltage of the non-aqueous electrolyte.
This is because if the oxidation potential is lower than the charging voltage, charging becomes impossible, and if the oxidation potential is higher than the decomposition voltage of the non-aqueous electrolyte, the decomposition of the non-aqueous electrolyte cannot be suppressed.

[0013] The addition ratio of the non-aqueous electrolyte solution of the azo compound varies slightly by the total amount of non-aqueous electrolyte in the battery, usually 1 × 10 ^-3 mol on include a significant effect of adding /
It is necessary to add more than 1 liter. 0.01 to 1 mol /
It is preferable to add in the range of liter. When the addition ratio is less than 0.01 mol / l, the effect of addition is not sufficiently exhibited, and when it exceeds 1 mol / l, the conductivity decreases due to the relative decrease in the amount of the electrolyte. This is because the storage characteristics and the cycle characteristics tend to decrease due to the excessive azo compound reacting with the positive electrode or the negative electrode gradually.

In the present invention, lithium metal or a substance capable of inserting and extracting lithium is used as the negative electrode material. Examples of the substance capable of inserting and extracting lithium include lithium alloys, graphite, and carbon materials such as coke.
Graphite is particularly preferred in that it has a large lithium storage / release amount (capacity).

As the positive electrode material (active material) in the present invention, for example, oxides of metals such as manganese, cobalt, nickel, vanadium and niobium which are conventionally used in non-aqueous electrolyte batteries having a battery voltage of 3 V or more. (LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ etc.)
Alternatively, a composite oxide containing two or more of these metals (Li
Ni _x Co _1-x O ₂ (however, 0 <x <1) or the like.

The effect of the present invention is remarkably exhibited when a high potential type positive electrode material which has a high potential and easily induces decomposition and degradation of the non-aqueous electrolyte is used, but is used as an additive to the positive electrode active material. The azo compound also has a function of suppressing the decomposition and degradation of the non-aqueous electrolyte during overcharging, so that the positive electrode material of the present invention exhibits a high potential of 3 V or more in a normal state (during storage or normal charging). It is not necessarily limited to the material.

The present invention is characterized in that an azo compound is added to a non-aqueous electrolyte to make it less likely to decompose and deteriorate in order to obtain a non-aqueous electrolyte battery having excellent battery characteristics such as storage characteristics and cycle characteristics. Therefore, other members constituting the battery such as the non-aqueous electrolyte are not particularly limited, and various materials conventionally used or proposed for non-aqueous electrolyte batteries can be used without any particular limitation. is there.

For example, as the solvent of the non-aqueous electrolyte, organic solvents such as ethylene carbonate, vinylene carbonate and propylene carbonate, and dimethyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, etc. And a low-boiling solvent such as ethoxymethoxyethane.

The solutes of the nonaqueous electrolyte include lithium perchlorate (LiClO ₄ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium hexafluorophosphate (LiPF ₆ ), and lithium tetrafluoroborate. (LiBF _4), lithium hexafluoroarsenate (LiAsF _6), lithium hexafluoroantimonate (LiSbF ₆₎ are exemplified.

Incidentally, as the non-aqueous electrolyte in the present invention, it is possible to use a solid electrolyte instead of the above-mentioned liquid electrolyte.

[0021]

In the battery of the present invention, since at least one azo compound is added to the non-aqueous electrolyte, a reaction between the positive electrode active material and the non-aqueous electrolyte occurs even when the battery is stored for a long time or overcharged. It is difficult to decompose and degrade the non-aqueous electrolyte. The reason is presumed as follows.

That is, since the azo compound has a conjugated double bond in the molecule, the resonance stabilizing effect of the molecule is high. Therefore, when the positive electrode potential is increased by charging or the like, the azo compound is oxidized on the positive electrode side, as shown in the following chemical formula 3. To generate cations (cations). When the oxidation potential of the azo compound is lower than the oxidation potential of the non-aqueous electrolyte, the oxidation reaction of the azo compound shown in Chemical Formula 3 occurs in preference to the oxidation reaction of the non-aqueous electrolyte. In other words, the azo compound is sacrificed (dummy) and oxidized to suppress the decomposition of the solvent in the non-aqueous electrolyte. Since the azo compound has excellent reversibility of the oxidation-reduction reaction, the generated cation diffuses in the non-aqueous electrolyte, and is reduced on the negative electrode side as shown in the following chemical formula 4, and returns to the original azo compound again. , Is repeatedly used as a dummy for an oxidation reaction on the positive electrode side.

[0023]

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[0024]

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[0025]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples, and may be carried out by appropriately changing the scope of the present invention. Is possible.

Example 1 A flat nonaqueous electrolyte secondary battery was manufactured.

[Positive Electrode] As a positive electrode active material, manganese dioxide heated at 375 ° C. was used.
A carbon powder as a conductive agent and a fluororesin powder as a binder are mixed at a weight ratio of 85: 10: 5, and then this mixture is pressed and then heated at 250 ° C. to form a disc. Was produced.

[Negative Electrode] A disc-shaped negative electrode was prepared by punching a rolled lithium plate into a predetermined size.

[Electrolyte] Ethylene carbonate (EC)
In a mixed solvent of propylene carbonate (PC) and 1,2-dimethoxyethane (DME) in a volume ratio of 5: 3: 2, lithium trifluoromethanesulfonate (LiCF
₃ SO ₃ ) was further dissolved in a 1 M solution.
4′-Tetramethyldiaminoazobenzene was added at a rate of 0.01 mol / liter to prepare an electrolytic solution.

[Preparation of Battery] A flat type battery BA1 (outer diameter: 20 mm,
(Thickness: 2.5 mm). In addition, as a separator, a polypropylene microporous membrane (manufactured by Celanese Corporation,
(Trade name "Celgard"), which was impregnated with the electrolytic solution.

FIG. 1 is a cross-sectional view schematically showing the produced battery BA1 of the present invention. The battery BA1 of the present invention shown in FIG.
It comprises a positive electrode 1, a negative electrode 2, a separator 3 for separating the electrodes 1 and 2 from each other, a positive electrode can 4, a negative electrode can 5, a positive electrode current collector 6, a negative electrode current collector 7, an insulating packing 8 made of polypropylene, and the like.

The positive electrode 1 and the negative electrode 2 are housed in a battery case formed with positive and negative bipolar cans 4 and 5 facing each other via a separator 3 impregnated with an electrolytic solution. The negative electrode 2 is connected to the negative electrode can 5 via the negative electrode current collector 7 and the negative electrode 2 is connected to the negative electrode can 5 by passing chemical energy generated inside the battery as electric energy from both terminals of the positive electrode can 4 and the negative electrode can 5. It can be taken out.

Example 2 A battery BA2 of the present invention was produced in the same manner as in Example 1 except that lithium hexafluorophosphate was used instead of lithium trifluoromethanesulfonate as a solute of the electrolytic solution.

Example 3 As the solvent for the electrolytic solution, ethylene carbonate, propylene carbonate and ethoxymethoxy were used instead of a mixed solvent of ethylene carbonate, propylene carbonate and 1,2-dimethoxyethane in a volume ratio of 5: 3: 2. Volume ratio with ethane (EME) 5: 3:
Battery BA3 of the present invention was produced in the same manner as in Example 2, except that the mixed solvent of No. 2 was used.

(Comparative Example 1) In the preparation of the electrolytic solution,
Comparative battery BC1 was prepared in the same manner as in Example 1 except that 4′-tetramethyldiaminoazobenzene was not added.
Was prepared.

Comparative Example 2 A comparative battery BC2 was produced in the same manner as in Comparative Example 1 except that lithium hexafluorophosphate was used instead of lithium trifluoromethanesulfonate as a solute of the electrolytic solution.

(Comparative Example 3) As the solvent for the electrolytic solution, ethylene carbonate, propylene carbonate and ethoxy methoxy Volume ratio with ethane (EME) 5: 3:
Comparative Battery BC3 was made in the same manner as Comparative Example 2 except that the mixed solvent of No. 2 was used.

[Cycle characteristics] At room temperature (25 ° C.)
A charge / discharge cycle test was performed in which a charge-discharge cycle test was performed in which a step of discharging at 4 mA for 2 hours at 1 mA was performed after charging at a charge end voltage of 3.5 V at mA, and the cycle characteristics of each battery were examined. The time when the discharge voltage reached 2.4 V within the discharge time was determined as the life of each battery, and the charge / discharge cycle test was terminated at that time. The results are shown in FIGS. 2, 3 and 4.

FIGS. 2 to 4 show cycle characteristics of each battery.
The vertical axis represents the discharge end voltage (V) in each cycle, and the horizontal axis represents the number of cycles (times).
From these figures, it can be seen that the batteries BA1 to BA3 of the present invention in which 4,4′-tetramethyldiaminoazobenzene was added to the electrolytic solution.
It can be seen that, compared to the comparative batteries BC1 to BC3 which did not add it, the cycle life was longer and the cycle characteristics were excellent because the degradation of the electrolytic solution was small.

[Overcharge Characteristics] Ten batteries each of the battery BA1 of the present invention and the comparative battery BC2 were prepared, and the battery voltage of each battery was reduced to 4V, which is higher than the normal charge end voltage.
The battery was held for 0 days (overcharged state), and changes in the internal impedance and the battery thickness of each battery at that time were examined. Table 1 shows the results.

[0041]

[Table 1]

As shown in Table 1, the battery BA1 of the present invention
As compared with the comparative battery BC2, the degradation of the electrolytic solution is small, so that the increase in the internal impedance and the increase in the thickness of the battery in the overcharged state are generally small and the reliability is high.

(Examples 4 to 7) In place of 0.01 mol / l of 4,4'-tetramethyldiaminoazobenzene, 4,4'-tetraethyldiaminoazobenzene,
4,4′-tetrapropyldiaminoazobenzene, 4,
4'-tetrabutyldiaminoazobenzene or 4,4 '
-Batteries BA4 to BA7 of the present invention were produced in the same manner as in Example 1 except that tetraphenyldiaminoazobenzene was used in the same ratio.

[Cycle Characteristics] A charge / discharge cycle test was performed under the same conditions as above, and the cycle characteristics of each battery were examined. The results are shown in FIG. 5, which is a graph in the same coordinate system as in FIGS. In the figure, the cycle characteristics of the comparative battery BC1 are also shown for comparison. From the figure, it is understood that the batteries BA4 to BA7 of the present invention in which the azo compound was added to the electrolytic solution had a longer cycle life and were superior in cycle characteristics as compared with the comparative battery BC1 in which nothing was added.

In the embodiments described above, the case where the present invention is applied to a flat prismatic type non-aqueous electrolyte battery has been described as an example. However, the shape of the battery is not particularly limited, and various shapes such as a cylindrical type and a square type are available. The present invention can be applied to a non-aqueous electrolyte battery having the following shape.

In the above embodiment, the case where the present invention is applied to a secondary battery has been described. However, since the present invention battery has a small increase in internal impedance and a small increase in battery thickness in an overcharged state, the present invention is not limited to this. Can be suitably applied to a primary battery for memory backup stored in an overcharged state.

[0047]

According to the battery of the present invention, since the azo compound is added to the non-aqueous electrolyte, the non-aqueous electrolyte is hardly decomposed and degraded, and thus has excellent battery characteristics such as storage characteristics and cycle characteristics. Has an excellent specific effect.

[Brief description of the drawings]

FIG. 1 shows a flat nonaqueous electrolyte battery (battery BA of the present invention).
It is sectional drawing of 1).

FIG. 2 is a graph showing cycle characteristics of a battery BA1 of the present invention and a comparative battery BC1 manufactured in Examples.

FIG. 3 is a graph showing cycle characteristics of a battery BA2 of the present invention and a comparative battery BC2 produced in Examples.

FIG. 4 is a graph showing cycle characteristics of a battery BA3 of the present invention and a comparative battery BC3 produced in Examples.

FIG. 5 is a graph showing cycle characteristics of batteries BA4 to BA7 of the present invention and a comparative battery BC1 manufactured in Examples.

[Explanation of symbols]

 BA1 Non-aqueous electrolyte battery (battery of the present invention) 1 Positive electrode 2 Negative electrode 3 Separator

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Toshihiko Saito 2-18-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (56) References JP-A-6-223875 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 10/40 H01M 6/16

Claims (2)

(57) [Claims] 1. A non-aqueous electrolyte battery comprising a negative electrode using metal lithium or a substance capable of inserting and extracting lithium as a negative electrode material, a positive electrode, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte is represented by the following formula 1. A non-aqueous electrolyte battery characterized by adding an azo compound. Embedded image (However, R ¹ , R ² , R ³ , and R ⁴ are each independently a hydrogen atom or a hydrocarbon group.) 2. The method of claim 1, wherein the azo compound is 4,4'-tetramethyldiaminoazobenzene, 4,4'-tetraethyldiaminoazobenzene, 4,4'-tetrapropyldiaminoazobenzene, 4,4'-tetrabutyldiaminoazobenzene, and The non-aqueous electrolyte battery according to claim 1, wherein the non-aqueous electrolyte battery is at least one azobenzene derivative selected from the group consisting of 4,4'-tetraphenyldiaminoazobenzene.